In January 2017, NASA's Curiosity Mars Rover stumbled upon what looked like ancient mud cracks in the Martian soil inside Gale Crater. Photos of a 30-inch-long slab of rock nicknamed "Old Soaker" captured by the Curiosity Mastcam showed it was covered in a crisscross pattern of polygons that bore a striking resemblance to desiccation cracks normally found on Earth.
Geologists at the California Institute of Technology (Caltech) in Pasadena have spent the last year analyzing those features and are finally able to confirm the polygons on Old Soaker are remnants of an ancient lake that dried up 3.5 billion years ago.
In a study published last week in the journal Geology, the Caltech researchers provide evidence that the mud cracks found on Mars are indeed desiccation cracks and that they were formed by the exposure to air of wet sediment.
"We are now confident that these are mud cracks," lead author Nathaniel Stein said in a press release by The Geological Society of America.
His team used the Curiosity rover to gather as much data as possible about the physical appearance and the chemical composition of Old Soaker. The ancient slab of rock, no bigger than a coffee table, was examined in detail by means of the rovers' Mastcam, Mars Hand Lens Imager, ChemCam Laser Induced Breakdown Spectrometer (LIBS), and the Alpha-Particle X-Ray Spectrometer (APXS), shows the press release."The Curiosity Rover is an amazing tool because it is acting as a robotic field geologist, piecing together the clues left from an ancient lake system," Stein said in a statement for Newsweek.
The data revealed that the ridges and cracks found on the red-toned Martian rock were formed by ancient sediment accumulated over time in the drying lake that was once Gale Crater. The analysis also concluded that the desiccation mud cracks were formed by exposure to air, and not by heat or the natural flow of water, notes the press release.
Since Old Soaker was discovered not on the edge of Gale Crater but rather closer to the center of the ancient lake bed — the Curiosity Rover detected the slab of rock in the Sutton Island member of the Murray formation, the study points out — the position of the mud cracks suggests that lake levels fluctuated dramatically over time.
The mud cracks "indicate a transition from longer-lived perennial lakes recorded by older strata to younger lakes characterized by intermittent exposure," the study authors write in their paper.
This discovery sheds new light into the ancient climate of the Red Planet, Stein explains.
"The mud cracks show that the lakes in Gale Crater had gone through the same type of cycles that we see on Earth."According to Stein, the mud cracks uncovered by the Curiosity Rover "are exciting because they add context to our understanding of this ancient lacustrine system."